Question

When does electron capture emit gamma rays?

Answer 1

No gamma rays are emitted in electron catpure.

Explanation:

Primary
Electron capture (EC) is a process that competes with positron (`beta^+`) emission. In EC the unstable nucleus captures an orbital electron, usually from the shell closest to the nucleus (K-shell). The nucleus emits a `color(blue)"neutrino"`.

Secundary
EC leaves a vacancy in the shell from which the electron was captured. This can be filled with electrons dropping down from a higher-level. This releases energy in the form of a photon classified as `color(blue)"characteristic X-ray"`. It is also possible that the energy is not emitted as a photon, but is transfered to another electron in a higher shell. The emitted electron in this process is called an `color(blue)"Auger electron"`.

Note that although gamma rays and X-rays are both photons, they are not the same. Gamma rays originate from processes in the nucleus en X-rays originate from the surrounding electron shells.